CMU Artificial Intelligence Repository     ## DCTG: Prolog definite clause translation grammar translator.

```lang/prolog/code/syntax/dctg/
```
Definite Clause Translation Grammars are described in chapter 9 of Abramson and Dahl's book "Logic Grammars". They were devised by Abramson to overcome the defects of Definite Clause Grammars, in which syntax and semantics are often mixed in a non-modular fashion. They avoid also the problem with the proliferation of unnamed arguments that afflicts Definite Clause Grammars. In a DCTG, the syntax and semantics are separated. Each rule contains first a syntactic part, and then an optional semantics, written as one or more clauses. An example is given below. See Ambramson and Dahl's book for more details. The code in this package comes from Appendix II of the book, with a few minor changes by Jocelyn Paine. The following example shows how to parse binary numbers with binary points (such as 1.1 or 1001.11) when expressed as lists ([1,'.',1] or [1,0,0,1,'.',1,1]). bit ::=  <:> bitval( 0, _ ). bit ::=  <:> bitval( V,Scale ) ::- V is **(2,Scale). bitstring ::= [] <:> length(0) && value(0,_). bitstring ::= bit^^B, bitstring^^B1 <:> length( Length ) ::- B1 ^^ length(Length1), Length is Length1 + 1 && value( Value, ScaleB ) ::- B ^^ bitval( VB, ScaleB ), S1 is ScaleB - 1, B1 ^^ value( V1, S1 ), Value is VB + V1. number ::= bitstring ^^ B, fraction ^^ F <:> value(V) ::- B ^^ length(Length), S is Length-1, B ^^ value( VB, S ), F ^^ fractional_value( VF ), V is VB + VF. fraction ::= ['.'], bitstring ^^ B <:> fractional_value( V ) ::- S is -1, B ^^ value( V, S ). fraction ::= [] <:> fractional_value(0). test( L, V ) :- write( 'LIST ' ), write( L ), nl, number( Tree, L, [] ), Tree ^^ value( V ), write( 'VALUE ' ), write( V ), nl, nl. ?- test( [1,'.',1], V ). /* Should set V to 1.5. */
```Origin:

src.doc.ic.ac.uk:packages/prolog-pd-software/ (146.169.2.1)
as dctg.tar.Z
```

Version: 21-JUL-90 Ports: Edinburgh-compatible Prologs. CD-ROM: Prime Time Freeware for AI, Issue 1-1 Author(s): Harvey Abramson and Veronica Dahl Keywords: Authors!Abramson, Authors!Dahl, Books!Prolog, DCG, DCTG, Definite Clause Grammar, Definite Clause Translation Grammar, Prolog!Code, Prolog!Syntax, Syntax References: Harvey Abramson and Veronica Dahl, "Logic Grammars", Springer Verlag, 1989.
Last Web update on Mon Feb 13 10:34:00 1995
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